Urethanes are produced by the reaction of hydroxyl compounds with isocyanates. The reactions are typically catalyzed with a tin or bismuth catalyst. When the hydroxyl and isocyanate compounds are mixed in the presence of the catalyst, the reaction proceeds rapidly to form a cured urethane product. This rapid curing of the urethane requires that the urethane composition be used quickly before the urethane cures leading to short working times (pot life). Lesser amounts of catalyst can be utilized to lengthen the time it takes for the urethane composition to cure which in turn allows for longer pot life for the composition. This approach can lengthen the cure time such that it slows the production of products that utilize the urethane compositions. Ideally, a urethane composition should be storable and usable for a long period then curable on demand.
Approaches that passivate the curing catalyst with a passivating agent that can be subsequently neutralized are described in U.S. Pat. Nos. 4,788,083, 5,478,790, 6,348,121 and 6,548,615. In this approach, neutralization of the catalyst passivator activates the catalyst so that the urethane composition can cure. The specific passivating agent and the mechanism for neutralizing the passivator determine the rate at which a urethane composition will cure.
If the passivating agent is not effective enough, the urethane can cure prematurely. If the mechanism for neutralizing the passivating agent is too slow, then the urethane can cure too slowly. Ideally, the passivator is effective in inhibiting the catalyst activity for long periods and the passivator should be capable of being neutralized quickly so that the maximum amount of catalyst is available immediately for a fast cure time.